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Most hairline cracks in the body tenons and bell are caused by impact with hard objects or mechanical stress created
during assembly,especially if the metal retaining rings have become loose. Barrels are similarly vulnerable,
but are also subjected to a great deal of moisture. If the wood is not sealed this moisture will dissolve the natural
oils and resins in the wood. Over time, the wood will contract in the bore, which creates internal stresses. Eventually,
the wood fibers will separate, the resulting crack, which woodworkers call a 'check', will be widest in the bore and
diminish toward the exterior. Once a check develops, more wood surface is exposed to moisture and erosion proceeds at
an accelerated pace. Unlike mechanical stress cracks, these checks change the shape of the bore. The relationship
between the separated wood fibers is changed such that they will never realign. These checks can only be repaired by
filling. In advanced cases reboring will be required. Mechanically created hairline cracks can be very effectively
repaired with superglue. The resulting bond has been proven to be stronger than the natural bond between wood fibers.
Checks can be effectively filled with a mixture of wood dust and epoxy or superglue.
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Loose rings are caused by a different, but related, process. The natural oils and resins in the wood decompose
over time. These are released as gases. This decomposition is fairly uniform throughout the wood, so it does not
create stresses that result in cracks or checks. The wood simply shrinks. This process is substantially accelerated
by heat. Above 90-100 degrees Fahrenheit these oils and resins become a lot more volatile. When wood burns, the heat
causes these substances to decompose into gases. It is these gases that actually combine with oxygen to make a flame.
You may have heard this shrinkage attributed to loss of moisture. Grenadilla wood is extremely resinous and dense. It has
adapted to live in semi-arid conditions and it is well seasoned before processing. The wood fibers that transport water
and nutrients are right under the bark. These fibers die and become part of the tree's structure. Slowly the water is
replaced with oils and resins as the wood becomes heartwood. Only seasoned heartwood is used for wind instruments.
There is virtually no moisture to be lost. While all wood will respond to changes in relative humidity, the dimensional
changes are inversely proportional to density. Even in much lighter woods the significance of these changes is limited
to large areas that are glued 'cross grain'. There are no glued or cross grain contacts in wood bodied wind instruments.
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Wood is, none the less, vulnerable to exposure to moisture, which cannot be avoided with mouth blown instruments.
While most of the water transportation channels have filled with oils and resins, some have not. These can be envisioned
as drinking straws. If not sealed, they will absorb some moisture. The greatest exposure is in the end grain, but some
of these 'pores' are exposed on all wood surfaces that are not cut strictly parallel with the grain. It is extremely
important to dry the bore and mortises of your instrument before it cools. Otherwise, the thermal contraction will draw
the moisture into any unsealed 'straws'. Each thermal cycle that occurs when playing will draw in more unless enough time
has passed to allow the moisture to evaporate (dry). Wood cells contain water when they are alive and retain much of
this water until the wood is cut and seasoned. During the seasoning process the cells will shrink to a certain extent
which varies between species. The cell walls are permeable to both vapor and gas. As the water is lost, much of the
space it occupied is filled with air. The slower the seasoning process, the more this replacement occurs, which results
in less actual shrinkage. This minimizes creation of internal stresses. When wood is unsealed, it will tend to equalize
moisture content with its immediate environment. Exposure to moisture can thereby reverse the seasoning process. Each
time this cycle of gaining and losing moisture occurs, less replacement takes place and more shrinkage is likely.
Eventually, the internal stresses will build up and the wood fibers will separate, creating a 'check'.
- Bore oil will create a surface tension to resist moisture. It has several drawbacks. It is not fixed in place and
weighs less than water. It has a tendency to float and be carried off by the very substance it is intended to resist.
Further, it is very amenable to being absorbed into a drying swab along with the moisture being removed. It will often
migrate onto the pads causing discoloration and if there's enough of it, stickiness. It is a fifty cent solution to a
dollar problem. It really doesn't matter if it's vegetable or mineral.
- The best solution I've found is hardwood floor wax. It overcomes all of oil's shortcomings without compromising any
of oil's positive qualities. It seals open pores, creates surface tension to moisture, is fixed in position and it is
relatively durable as it will not abrade during a drying process. The major drawback is that application is tedious.
The key work must be removed and it takes over 30 minutes to apply and buff. Still, if the bore appears dull, it needs treatment.
For regular maintenance, oil maybe the only practical option. However, the barrel is the most vulnerable and can be easily waxed.
- Almost all clarinet keywork is made by forging a nickle/copper alloy and over-plating with pure nickel or silver.
- Forging is shaping metal that has been heated to improve malleability. Hand forging is what the blacksmith does.
Drop forging employs a very heavy weight that is lifted by a motor instead of a hammer. 'Power' forging replaces both
with hydraulic pressure. Although power forging may have a cost advantage for large quantities, none of these methods
inherently produces a superior result.
- Nickel is hard and strong, but by itself, it is too brittle for forging. Copper is added to overcome this. It also
makes the work more likely to bend instead of break when subjected to stress.
- Keywork is plated with pure nickle or silver for mostly cosmetic purposes. When we contact the keywork small
electrical circuits are created. This creates an electrolytic pathway and the copper ions migrate toward
our fingers. This effect is more pronounced in some people. Unplated nickle/copper alloy always has a slight yellow
color, which increases substantially with this migration. So much that it is called 'brassing'. Plating greatly reduces
this migration, but may not stop it entirely. Sometimes what is commonly called 'plating wear' is copper that has
migrated through the plating. This copper can easily be removed from both plated and unplated keywork.
- Nickel does tarnish. This is the most common reason why keywork requires power buffing. It is also a major cause
of 'plating wear'. The tarnish is caused by exposure to environmental contaminants which are usually airborne. The
contaminates combine with the nickel and the resulting compound can often be removed by the friction of our fingers on
the keys. Silver tarnish is caused by it's combination with sulfides and can be chemically reversed without loss of
silver. Plating loss is not only the result of friction induced 'wear' of tarnish. It is also the result of nickle or
silver ions migrating from the work to our skin. Eventually the reserve of ions is depleted and the underlying
alloy is exposed.
- Plating erosion is also caused by salts and acids that are deposited when our skin sweats. It can also be caused by
other substances that have been inadvertently deposited and not removed. This process is usually uneven and results in
pitting. On plated work, once these pits occur they tend to capture and retain these salts and acids. Because copper
corrodes more readily than nickle or silver the corrosion tends to travel under the surrounding plating. As metals
oxidize, or combine with other elements, they take up more room, which forces the plating from the underlying work.
This is why pits often appear to have erupted from below. It is possible to fill and replate over pits but it is usually more
cost effective to replace the keywork. If more than one, two or maybe three parts need to be replaced, it will cost
more than can be justified unless a donor instrument is available.
- Anti-tarnish cloths work well with silver and may help with nickel to reduce or prevent tarnish. Pitting can be
prevented by wiping the finger touches, preferably with a damp cloth. This is most effective after playing while your
hands have been sweating. Unfortunately, there is no practical way to prevent electrolytic ion migration. Overall,
plating erosion can be slowed, but not prevented.
- Sometimes a layer of pure copper is plated over the alloy. This improves the speed of deposition of the top plate.
It is not required over a nickle base, but is needed if key is cast from 'pot metal'. It has several undesirable effects.
It makes the top plate more susceptible to damage from impact or bending, which will cause the plating to peel. If the
top layer is eroded, it looks ugly and the copper layer will erode very quickly which results in an edge that can often
be felt. When there is a copper layer, replating is the only effective option and the sooner it is done, the better the
result will be.
- If no copper layer is present, the alloy will erode at a similar rate to a nickel top plate, so nothing must be done
and polishing will keep the work looking good. There is a somewhat greater color difference between silver and
nickel/copper alloy, but the alloy will erode at a slower rate. Silver plating is more likely to be plated over a copper
layer, which is very unattractive when exposed.
- We used to replate with silver. This is a relatively easy but time consuming process. It is suitable for small requirements.
When polished, it is difficult to tell the difference between nickel and silver, but silver will tarnish more readily.
Despite many attempts to to achieve a long lasting result, using various chemical solutions, we no longer replate or recomend
replating. A good looking result can be achieved, but it will wear quickly with use.
- Cast keywork is problematic. It will bend more easily under stress but will also break more easily. Once it is bent
attempting to restore it to a functioning shape will often cause the work to break. If it doesn't break then, it will
leave it substantially more vulnerable to breakage under stress. Once broken it cannot be repaired. It also wears
at pivots and axles more quickly. The wear cannot be compensated. The plating requires an undercoat of copper and is
more easily damaged, but impossible to replate. There is a huge cost advantage over forging as both the material used
and the process are less costly. But, even if replacement parts are available, it is not cost effective to repair
instruments with damaged cast keywork. Often when there is no damage is apparent some adjustment by bending is required
for proper functioning. Why would anyone want to take the risk that goes with repairing these instruments? I don't.
- Selmer Soloist clarinets that aren't silver plated have a layer of chrome added over the nickel. It gives a blue tint
to the work. Chrome is very hard, will prevent electrolytic migration and is very corrosion resistant. Still, salts
and acids left on the surface will eventually do their dirty work. Chrome cannot be over-plated and must be removed
before replating is done.
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